In most data recording and retrieval operations today, a Winchester type of magnetic head technology is used which traces its beginnings to a design developed by IBM Corporation in the early 1970's. Although there have been numerous variations and improvements over the intervening years, the fundamental design has included a spring loaded head-flexure mechanism maintained at a substantially constant distance, or flying height, from a rotating magnetic media.
Although the Winchester disk drive has become ubiquitous in the computing environment, a major limitation of such disk drives has been their general lack of portability. One of the major limitations on portability has been the limited shock resistance available with conventional designs. Most portability issues deal with shock during power-down, or while power is removed.
In nearly all current designs for Winchester disk drives, shock resistance is a major design consideration. Despite such efforts, shocks imparted to a drive as the result of being dropped, hit, jiggled, or by other movement are known to cause serious damage to the drive. Many design efforts have been attempted to reduce problems with shock, and substantial strides have been made compared to the extremely fragile designs of a few years ago. Auto-parking designs have been developed to position the heads in a "safe" location when power is turned off, but this alone does not always prevent damage when a drive is dropped. Head latches have been developed to work with auto-parking to fixedly position the heads in a safe location during powerdown, and this has allowed shock resistance to be improved significantly.
However, head latch implementations normally represent a tradeoff between between the amount of power which can be supplied to release the heads during power-up, and the number of G's shock resistance provided by the head latch to prevent the heads from sliding across and scoring the media. As a result, head latches have proven insufficient to provide the kind of significant shock or impact protection required to allow an external drive subsystem to survive the hazards of day-today operation in a home or office environment.
One measure of the limits of current impact resistant designs is that virtually no current drive design for general commercial use provides shock resistance capable of withstanding a thirty inch fall onto a concrete floor--an all-too-common occurrence in everyday life.
Another approach to impact resistance has been the removable media drive. Removable media drives such as those produced by lomega and SyQuest have attempted to solve shock problems in a portable environment by simply arranging for the removal of the media during power-off. In these designs, a fixed head stack remains in a housing, while the media cartridge is removed. This allows for both shock resistance--because there are no heads in the cartridge to cause damage should the cartridge be dropped, and for enhanced capacity by swapping cartridges. While this has a number of initially attractive aspects, the lack of a sealed environment has created serious limitations for removable media drives which impact their ability to provide a long term solution. More specifically, a typical cartridge design is required to be exposed--at least some of the time--to the ambient environment, which is typically dust-laden or--even worse, rich in propellants and pollutants from hair or other sprays. The deposition of any such materials--even in relatively minute quantities from the perspective of the user--on the media of a removable cartridge has been known to lead to disastrous results including loss of data or complete failure of the cartridge and drive. Moreover, the lack of a protected environment limits the data density possible on removable cartridges, in turn leading to a relatively poor price/performance ratio. The difficulties with removable cartridge drives are compounded by the continuing cost reductions in the conventional disk drive industry.
As a result, there has been a need for a disk drive subsystem which can offer the portability as good or better than a removable cartridge drive, while at the same time offering the data density and other advantages of a fixed disk system.